Additive for plating bath

ABSTRACT

A plating bath additive and a plating bath using the said additive are provided, which plating bath contains a hydroxyalkanesulfonic acid and which even when applied to an electronic part such as a semiconductor device does not give rise to a problem such as circuit-to-circuit insulation becoming defective. The plating bath additive contains a hydroxyalkanesulfonic acid as a main component and has an alkali metal content of less than 0.05 mass % relative to the hydroxyalkanesulfonic acid. The plating bath incorporates the said additive therein.

FIELD OF THE INVENTION

The present invention relates to a plating bath additive containing ahydroxyalkanesulfonic acid as a main component, as well as a platingbath using the said additive.

BACKGROUND OF THE INVENTION

Hydroxyalkanesulfonic acids have heretofore been used as a component ofvarious plating baths. For example, in JP 53-14131A, ahydroxyalkanesulfonic acid is used as a plating bath component for theformation of tin-lead alloy electroplating so as to serve as a film forimproving solderability or as an etching resist film.

In JP 11-1792A it is disclosed that a hydroxyalkanesulfonic acid is usedas a plating bath component for plating to an electronic part or forforming Pb—Sn alloy salient electrodes onto a surface of a semiconductorwafer.

In JP 11-279787A it is disclosed that a hydroxyalkanesulfonic acid isused as a plating bath component for silver or silver alloy plating.

In JP 2000-87252A it is disclosed that a hydroxyalkanesulfonic acid isused as a plating bath component for an electroless tin-bismuth alloyplating bath.

However, for example isethionic acid as a conventionalhydroxyalkanesulfonic acid is obtained as sodium salt by subjectingethylene oxide to the action of sodium hydrogen sulfite (seeEncyclopaedia Chimica, Vol. 1, page 581), which is then ion-exchanged toremove the alkali metal for use as an acid.

On the other hand, when plating an electronic part such as asemiconductor device in a plating bath containing ahydroxyalkanesulfonic acid, there sometimes has occurred a problem thatcircuit-to-circuit insulation in the electronic part is defective.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide aplating bath additive and a plating bath using the said additive, whichplating bath contains a hydroxyalkanesulfonic acid and which even whenapplied to an electronic part such as a semiconductor device does notgive rise to a problem such as circuit-to-circuit insulation becomingdefective.

Having made earnest studies in view of the above-mentioned point, thepresent inventors found out that if an alkali metal was present within aplating bath, the alkali metal remained even if the surface of a platedarticle after plating was subjected to cleaning having such aneconomical characteristic as falling under an industrially allowablerange, thus sometimes resulting in circuit-to-circuit insulation in theelectronic part becoming defective. In this way we accomplished thepresent invention.

More specifically, the present invention resides in a plating bathadditive containing a hydroxyalkanesulfonic acid as a main component,characterized in that the content of an alkali metal relative to thehydroxyalkanesulfonic acid is less than 0.05 mass %.

The present invention also resides in the above plating bath additivewherein the hydroxyalkanesulfonic acid is isethionic acid.

The present invention further resides in the above plating bath additivewherein the hydroxyalkanesulfonic acid is obtained by a method involvingoxidizing a hydroxyalkylmercaptan with use of hydrogen peroxide.

The present invention further resides in a plating bath using the aboveadditive.

According to the present invention there are provided a plating bathadditive and a plating bath using the said additive, which plating bathcontains a hydroxyalkanesulfonic acid and which even when applied to anelectronic part such as a semiconductor device does not give rise tosuch a problem as circuit-to-circuit insualtion in the electronic partbecoming defective.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The plating bath additive according to the present invention contains ahydroxyalkanesulfonic acid as a main component, with the content of analkali metal relative to the hydroxyalkanesulfonic acid being less than0.05 mass %.

The hydroxyalkanesulfonic acid component is not specially limited.Compounds represented by the general formula HO—R—SO₃H are preferredwherein R is a hydrocarbon group having 1 to 12 carbon atoms and thehydroxyl group may be located at any position of R. Concrete examplesare 2-hydroxyethane-1-sulfonic acid (isethionic acid),2-hydroxypropane-1-sulfonic acid, 1-hydroxypropane-2-sulfonic acid,3-hydroxypropane-1-sulfonic acid, 2-hydroxybutane-1-sulfonic acid,4-hydroxybutane-1-sulfonic acid, 2-hydroxypentane-1-sulfonic acid,2-hydroxyhexane-1-sulfonic acid, and 2-hydroxydecane-1-sulfonic acid.Particularly, 2-hydroxyethane-1-sulfonic acid (isethionic acid) ispreferred as the plating bath additive.

How to prepare the hydroxyalkanesulfonic acid is not specially limited.Reference will now be made to isethionic acid as an example. Isethionicacid can be obtained by a conventional method involving subjectingethylene oxide to the action of sodium hydrogensulfite to afford sodiumsalt and subsequent ion exchange to remove an alkali metal component. Inthis case, the ion exchanging operation is repeated until the alkalimetal content becomes less than 0.05 mass % relative to thehydroxyalkanesulfonic acid.

The method disclosed in JP 10-204052A, which involves oxidizing ahydroxyalkylmercaptan with use of hydrogen peroxide, is preferredbecause an alkali metal is not used and therefore ahydroxyalkanesulfonicacid with an alkali metal content of less than 0.05 mass % can beobtained more effectively.

The plating bath additive according to the present invention is usefulas a hydroxyalkanesulfonic acid component added to the plating bath andthe hydroxyalkanesulfonic acid content in the plating bath additive isarbitrary. Any other desired components than the hydroxyalkanesulfonicacid may be added into the plating bath of the present invention,provided it is necessary to make a control so that the alkali metalcontent relative to the hydroxyalkanesulfonic acid does not become 0.05mass % or more.

Other components which may be added-into the plating solution are notspecially limited. As examples of such other components there arementioned antioxidants (e.g., catechol, hydroquinone, ascorbic acid),brighteners or brightening aids (e.g., benzaldehyde, formalin, glyoxal),complexing agents (e.g., EDTA, ethylenediamine, citric acid), nonionicsurfactants as homogenizers (e.g., polyethylene glycol,oxyethylene-oxypropylene block copolymer, alkylphenol ethylene oxideadducts, polyhydric alcohol fatty acid esters, fatty acid alkanolamides), and antioxidation aids or smoothing agents (e.g., thiourea,ethylene thiourea, thioglycolic acid).

The plating bath according to the present invention contains the platingbath additive described above. As other components than ahydroxyalkanesulfonic acid, components so far known as components of aplating path containing a hydroxyalkanesulfonic acid may be used inrespective known ranges.

Thus, arbitrary components may be selected for the plating bath of theinvention as desired by a user, with no special limitation being placedthereon. As examples of such components, mention may be made ofcompounds (e.g., copper, tin, silver, and their salts and oxides, eachalone or in combination of two or more) which supplies ions of a metalto be plated, inorganic acids, organic acids, oxidizing agents, reducingagents, surfactants, pH adjustors, pH controllers, buffer agents,smoothing agents, stress relaxation agents, stabilizers, complexingagents (chelating agents), brighteners, semibrighteners, antioxidants,dispersants, homogenizers, and other additives known to be incorporatedin plating baths. Arbitrary components which may be incorporated in theplating bath additive of the present invention are also capable of beingincorporated in the plating bath of the invention.

EXAMPLES

The present invention will be further described below by way of workingExamples thereof, but it is to be understood that the present inventionis not limited by the following Examples.

Example 1

357 g (6.3 mol) of 60 mass % hydrogen peroxide was charged into a glassreactor equipped with an internal condenser, an agitator, a condenserhaving an opening/closing cock for solvent distillation, and a liquidintroducing device, and thereafter 156 g (2.0 mol) of 2-mercaptoethanolwas fed continuously from a liquid inlet at a rate of 0.4 mL/min underagitation. During this operation, the liquid temperature was held at 45°C. by adjusting the amount of cooling water fed to the condenser. Afterthe end of the addition of 2-mercaptoethnaol, the agitation wascontinued at room temperature for 10 hours. Then, nitrogen gas was blowninto the reaction solution through a sample inlet pipe and the reactionsolution was held for 5 hours under heating at 110° C. and at theatmospheric pressure, with agitation, while a portion of vapor wasallowed to be discharged to the exterior of the reaction system. Thisreaction solution was then passed through a 35 mm dia. tower chargedwith 200 mL of an ion exchange resin (Duolite A-561, a product ofSumitomo Chemical Co.), from the top of the tower and is therebypurified to afford 54.0 mass % of an isethionic acid solution (yield241.6 g: percent yield 95.9%). No alkali metal was detected from thisacqeuous isethionic acid solution (detection limit 10 ppb).

The aqueous isethionic acid solution was used as a plating bath additive(1).

Comparative Example 1 & Example 2

A 43 mass % aqueous solution of commercially available sodiumisethionate (a product of Aoki Yushi Kogyo Co.) was prepared and wasthen passed through a 30 mm dia. tower charged with 82 mL of an ionexchange resin (MONOSPHIA 630C_H, a product of The Dow Chemical Co.), ata (down-flow) SV1.0, from the top of the tower, and was thereby purifiedto afford 10 mass % of an aqueous isethionic acid solution having asodium content of 5 mass % relative to isethionic acid. The aqueousisethionic acid solution was then concentrated to an isethionic acidconcentration of 40 mass % and the thus-concentrated aqueous solutionwas used as a comparative plating bath additive (1).

After regeneration of the ion exchange resin by a conventional method,the same purifying operation as above was repeated twice for thecomparative plating bath additive (1) to afford a 7.0 mass % aqueousisethionic acid solution having a sodium content of 0.03 mass %. Thisaqueous isethionic acid solution was then concentrated to 40 mass % toafford a plating bath additive (2) according to the present invention.

Example 3

A 49.2 mass % aqueous 2-hydroxypropane-1-sulfonic acid solution wasprepared in the same way as in Example 1 except that 2-mercaptoethanolwas substituted by 2-mercaptopropanol. No alkali metal was detected fromthe aqueous 2-hydroxypropane-1-sulfonic acid solution.

The aqueous 2-hydroxypropane-1-sulfonic acid solution thus prepared wasused as a plating bath additive (3) according to the present invention.

Example 4 & Comparative Example 2

Using the plating bath additives prepared in Examples 1 to 3 accordingto the present invention and the comparative bath additive prepared inComparative Example 1, aqueous solutions of the composition shown inTable 1 were prepared as plating baths (Sn plating baths). TABLE 1 SnO 30 g/L Thiourea  8 g/L Additive for the plating baths 100 g/L (ashydroxyalkanesulfonic acid) p-Cumylphenol ethylene oxide  10 g/L (10mol) adduct Glyoxazole  1 g/L Catechol  1 g/L Balance Water

On the other hand, when two systems of adjacent copper circuits wereformed on a silicon wafer and were each Sn-plated using each of theplating baths prepared above, then tested for circuit-to-circuitinsulation. As a result, a satisfactory insulation was attained in caseof using the plating baths prepared according to the present invention,but the insulation was poor in the case of the plating bath using thecomparative plating bath additive prepared in Comparative Example 2.

1. A plating bath additive containing a hydroxyalkylkanesulfonic acid asa main component, characterized in that the content of an alkali metalrelative to the hydroxyalkylkanesulfonic acid is less than 0.05 mass %.2. A plating bath additive as set forth in claim 1, wherein thehydroxyalkylkanesulfonic acid is isethionic acid.
 3. A plating bathadditive as set forth in claim 1, wherein the hydroxyalkylkanesulfonicacid is prepared by oxidizing a hydroxyalkylmercaptan with use ofhydrogen peroxide.
 4. A plating bath containing the plating bathadditive described in claim
 1. 5. A plating bath containing the platingbath additive described in claim
 2. 6. A plating bath containing theplating bath additive described in claim
 3. 7. A plating bath additiveas set forth in claim 2, wherein the hydroxyalkylkanesulfonic acid isprepared by oxidizing a hydroxyalkylmercaptan with use of hydrogenperoxide.
 8. A plating bath additive as set forth in claim 4, whereinthe hydroxyalkylkanesulfonic acid is prepared by oxidizing ahydroxyalkylmercaptan with use of hydrogen peroxide.
 9. A plating bathadditive as set forth in claim 5, wherein the hydroxyalkylkanesulfonicacid is prepared by oxidizing a hydroxyalkylmercaptan with use ofhydrogen peroxide.
 10. A plating bath additive as set forth in claim 6,wherein the hydroxyalkylkanesulfonic acid is prepared by oxidizing ahydroxyalkylmercaptan with use of hydrogen peroxide.